Vehicle safety systems, including air bags and seat belt tighteners are conventionally triggered by various detection means and sensors, including acceleration detectors, that detect rapid decelerations and accelerations indicative of vehicle collision or impact. Further, attitude sensors to detect the angle of inclination of a vehicle serve an important safety function, including for example within all terrain, off-road or construction vehicles.
The term "vehicle" herein refers to all manner of craft for use on land or in air, water or space.
Conventionally, accelerometers comprise a frame, a mass, a spring-like supporting system for suspending the mass within the frame for relative movement within the frame, and damping means. Conventionally, an electronic circuit translates mechanical movement of the mass into an electrical signal. Most acceleration sensors operate mechanically with a displacement or vibration of a moveable arm detecting acceleration. These sensors measure displacement of an object from a specific reference point to obtain an acceleration value. Common acceleration sensors used in automotive safety restraint systems include capacitive, piezoresistive and piezoelectric sensors. A further type of system is the "reed switch", as disclosed within U.S. Pat. Nos. 3,587,011 and 5,594,400. In this arrangement, a pair of magnets are arranged in inverted polar orientations, producing opposed magnetic fields. A displacement of the reed switch results in a change of magnetic field, triggering the safety device.
Existing acceleration sensors suffer several drawbacks when implemented in connection with a vehicle safety system. In particular, many existing devices when conventionally manufactured have been found to have limited sensitivity to a crash event and suffer from an inability to be "fine tuned" to a particular acceleration level. While the sensitivity may be increased to a suitable level, this typically entails unacceptably high manufacturing costs. In the result, safety systems such as air bags are prone to deployment either too easily or the opposite.
In addition to acceleration sensors, other sensors exist which determine a vehicle's attitude. These sensors, which are well established within the aerospace industry, may be used to determine a vehicle's inclination for safety reasons. Conventional attitude sensors include a spherical ball suspended in an inert fluid, out of contact with a housing which encloses the assembly. The ball may include a magnet, whose orientation is affected by the earth's magnetic field. Monitoring the orientation of this magnet, which may be accomplished by the use of a pair of hall effect sensors positioned opposite to one another within the housing, permits an inclination reading. For example, see U.S. Pat. Nos. 5,452,519 and 5,356,671. A further prior art example is the linear servo accelerometer, which consists of a pair of accelerometers mounted on a horizontal plane at right angles to another. Any movement of the accelerometer from the normal horizontal plane is detected as movement along the vertical axis. See for example U.S. Pat. No. 3,808,697.
It is desirable to provide an improved acceleration and attitude sensor, providing within a single, relatively inexpensive unit an accurate and reliable detector of both acceleration and attitude. Such an apparatus may have applications for the triggering of safety devices in vehicles, and as well other useful applications within vehicles and other craft operating on land, water, air and space. Superior acceleration and attitude detection may be achieved through the use of a sensor which operates according to principles of detection of compression of a medium within which light or other wave energy is scattered, rather than strictly electrical or mechanical means.
Within applicant's previous PCT International application no. PCTCA98/00686 there is disclosed a pressure sensor which operates according to the principle whereby the intensity of light or other wave energy which is dispersed and scattered within an integrating cavity, is increased as the region within which the energy is dispersed is diminished. For example, as the medium is compressed, the scattering region is diminished, resulting in a detectable increase in the integrated or scattered light intensity. According to this principle, a pressure sensor may comprise a compressible carrier medium for light or other wave energy, containing scattering centers for disbursing the light within the carrier medium. Wave energy transmission and receiving means are associated with the carrier medium to transmit and receive, respectively, the wave energy to and from the carrier medium.
The term "light" will be generally used herein in reference to wave energy of any suitable type. It will be understood that other forms of wave energy including electromagnetic radiation in the non-visible spectra and sound may comprise the wave energy for use in the present invention.
The carrier medium may be enclosed within a compressible housing such as a flexible envelope or the like. Pressure applied to the housing compresses the carrier medium, thereby increasing the intensity of the light within the region surrounding the light source, in proportion to the decrease in volume. The change in light intensity is detected by the receiver, which transmits the information to a signal processing means. The carrier medium preferably includes multiple light scattering centers evenly disbursed throughout the medium. A suitable medium may be provided by a translucent foam material. Alternatively, the interior face of the enclosure may provide the light dispersion function. The enclosure comprises an integrating optical cavity, which is defined as a region or volume either bounded by an enclosure and comprising a deformable material with the characteristic whereby illumination within the cavity undergoes multiple scattering reflections or refractions to thereby become effectively randomized and smoothed out in its distribution throughout the cavity. In such a cavity, at the limit, information about the original direction of illumination is eventually lost and the light becomes fully scattered. An integrating optical cavity may be an air or gas filled enclosure, or may be a volume within by a translucent solid such as an open-cell or closed cell foam matrix that provides optical scattering sensors.
It is a characteristic of such a cavity that, for a light source with a constant power output, the light intensity within the cavity is a function of the volume of the cavity, the position of the light source and the reflectance of the walls of the envelope. The cavity may be formed with virtually any shape, although certain extreme shapes may not respond ideally.
A pressure sensor of this type may take several convenient forms that are adapted for the purposes of the present invention. For example, the sensor may comprise an elongate, flattened member featuring multiple light sources and receivers. Alternatively, the scattering medium may comprise a block of foam shaped to fit within a defined cavity or receiving space.